Method of electrodepositing ferromagnetic alloys

ABSTRACT

Deposition of cobalt-phosphorus and cobalt-nickel-phosphorus alloys, on conductive carriers, from an aqueous bath containing the metal ions and at least hypophosphite ions as the source of phosphorus. The deposition is solely the result of electrolysis. The aqueous bath has a pH of from 3.2 to 5.0. The current density is maintained in the range of 10 to 120 amperes per square foot. The products have magnetic properties rendering them valuable for application as high-density digital recording media. An improvement over the basic process involves the use of both phosphite ions and hypophosphite ions as the source of phosphorus. The phosphite ions decrease the concentration of hypophosphite ions required and increases stability of the electrolyte.

tilted States Patent Faulkner [54] METHOD OF ELECTRODEPOSITING FERROMAGNETIC ALLOYS [72] Inventor: John P. Faulkner, Thousand Oaks, Calif.

[73] Assignee: Burroughs Corporation, Detroit, Mich.

[22] Filed: .Ian. 29, 1969 [21] App1.No.: 795,054

Related U.S. Application Data [63] Continuation-in-part of Ser. No. 650,170, June 30, 1967, abandoned, which is a continuation of Ser. No. 229,723, Oct. 10, 1962, abandoned.

[52] U.S. Cl. ..204/43, 340/174 R, 340/174 TF [5]] lint. Cl. ..C23b 5/32, C23b 5/46 [58] Field of Search ..204/43, 44, 48, 49; 117/130 E; 340/174 TE [56] References Cited UNITED STATES PATENTS 3,219,471 11/1965 Chilton et a1. ..l17/47 3,227,635 l/l966 Koretzky et a1 204/28 2,026,718 1/1936 Weisberg et a1. 204/43 2,643,221 6/1953 Brenner et al. ...204/43 2,644,787 7/1953 Bonn et al ..204/43 2,921,888 l/l960 Halpert... ..204/48 X 3,138,479 6/1964 Foley ..106/1 3,202,590 8/1965 Koretzky ..204/43 FOREIGN PATENTS OR APPLICATIONS 51 Jan. 25, 1972 OTHER PUBLICATIONS Metal Finishing Guidebook Directory, pp. 360 and 658 (1960).

.1. Bagrowski et al., Jour. Electrochemical Soc., Vol. 109, No. 10, pp. 987- 988 (1962).

V. M. Zhogina et al., Soveschania p0 Electrokhimil, Soviet Electrochemistry, Proceedings of Fourth Conference on Electrochemistry, Authorized Translation from the Russian, New York Consultants Bureau, Vol. 3, pp. 40- 44( 1961).

Morton Schwartz, Proc. American Electroplaters Soc., Vol. 47, pg. 176(1960).

B. Ya. Kaznachei et al., Trudy Vsesoyuznogo Nauchnolssle Dovatel Skogo Instituta Zvukozapisi, No. 6, pp. 119- 135 1957).

I. Tsu, Plating, pp. 379- 381 (Apr. 1961).

I. Tsu, Plating, pp. 1207- 1210 (Nov. 1961).

V. Zentner, Plating, pp. 868-- 872 (Sept. 1965).

Primary ExaminerG. L. Kaplan AttorneyChristie, Parker & Hale [5 7] ABSTRACT Deposition of cobalt-phosphorus and cobalt-nickelphosphorus alloys, on conductive carriers, from an aqueous bath containing the metal ions and at least hypophosphite ions as the source of phosphorus. The deposition is solely the result of electrolysis. The aqueous bath has a pH of from 3.2 to 5.0. The current density is maintained in the range of 10 to 120 amperes per square foot. The products have magnetic properties rendering them valuable for application as high-density digital recording media.

An improvement over the basic process involves the use of both phosphite ions and hypophosphite ions as the source of phosphorus. The phosphite ions decrease the concentration of hypophosphite ions required and increases stability of the electrolyte.

41 Claims, No Drawings CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of copending patent application Ser. No. 650,l70 filed June 30, 1967 entitled Ferromagnetic Coatings which is a continuation of the patent application Ser. No. 229,723 filed Oct. 10, I962 entitled Ferromagnetic Coatings, both assigned to the same assignee as the present application both now abandoned.

BACKGROUND OF THE INVENTION 1 Field of the invention I This invention relates to ferromagnetic coatings and more particularly to an electrolytic method of depositing ferromagnetic coatings and the composition thereof. 1

2. Description of the Prior Art It is well known to record various types of information-audio, analog, and digitalon apparatus employing ferromagnetic coatings embodied in difierent forms; such as tape, disks, drums and the like, in which the ferromagnetic coating is applied as a film on a carrier formed of a nonferromagnetic material. The magnetic characteristics of the ferromagnetic coating determine the type and the amount of information of a given type which may be magnetically recorded thereon. When a ferromagnetic carrier is utilized for recording digital information, the important characteristic of the carrier is the amount of information that may be recorded on a given area of the carrier, or the allowable recording density. Digital computers handle large volumes of information at high speeds and this information is generally coded in binary form which may be recorded on a ferromagnetic coating embodied in one of the well known forms. A piece of binary information in a digital computer is generally identified as a bit" and these bits are usually recorded in tracks which are produced by the passage of a magnetic recording head over the ferromagnetic surface. As applied to a ferromagnetic coating, the number of bits per square inch of coating which may be recorded is an important factor in determining the cost of recording equipment. Since, in the design of recording equipment, there are mechanical considerations not associated with the characteristics of the ferromagnetic surface which place minimal limitations on the width of the recording track and on the distance between tracks, the recording density is generally specified as the number of bits per linear inch of recording track and stated in bits per inch. It will be recognized, then that the magnetic characteristics of a ferromagnetic coating for recording information are important as to the number of bits per inch which may be recorded and intelligently reproduced. To this end, an important characteristic of the ferromagnetic coating is the coercivity thereof. The recording information exists in the ferromagnetic coating as large numbers of very small magnetized areas and the presence of these magnetic poles induces within the surface of a field which tends to demagnetize these areas. Therefore, for any recording density, there is a minimum coercivity which must be maintained in the ferromagnetic coating to avoid the loss of information through this demagnetizing affect. As the recording density is increased, the number of magnetic poles is increased and the distances between poles is decreased, thus producing an increase in the demagnetizing field and an increase in the minimum coercivity which must be maintained in the ferromagnetic coating. With increasing coercivity, the minimum magnetic field produced by the recording head to achieve recording must be increased. Since reduction of the magnetic field to be produced by the recording head is of importance in the design of equipment for high speed recording and read-back, it is highly desirable that the coercivity of the ferromagnetic coating be controlled to provide a level which will minimize the effects of the self-induced demagnetizing field and, at the same time, will not be excessively great. Of course, other magnetic characteristics of the ferromagnetic coating are also of importance in determining the maximum recording density which may be achieved. Increasing the squareness ratio of the magnetic hystersis loop characteristic of the ferromagnetic coating results in a reduction in the minimum coercivity necessary to minimize the demagnetizing effect. With an increase in the remanence of the ferromagnetic coating, a proportional decrease in the thickness of the coating may be achieved without a decrease in the read-back signal amplitude. Since a reduction in the thickness of the ferromagnetic coating results in a reduction in the minimum magnetic field to be produced by the recording head and improved resolution of the recorded infonnation, the maximum obtainable remanence is to be desired. Therefore, for any given combination of recording head and recording mode, there is an optimum combination of coercivity, squareness ratio, remanence and thickness of the ferromagnetic coating.

A large amount of development work has been directed to improvement of the magnetic characteristics of ferromagnetic coatings for use as information recording media, particularly for recording binary coded information. In particular, it is known that electroplated coatings comprising alloys of cobalt with nickel provide advantageous properties, particularly from the standpoint of exhibiting high coercivities and remanences. In the development efforts reported along these lines, it is noted that the concensus of the investigators is that the coercivity of the deposited coating is controlled to a large degree by the composition of the alloy and, furthermore, that the maximum coercivity is achieved in alloys composed of 2530 percent of nickel. [t is also known that the coercivity of the electrodeposited alloy can be increased by the imposition of an alternating current component on the direct plating current. It has also been reported that the magnetic characteristics of a cobalt-nickel alloy coating may be improved by the addition of hypophosphite ions to the electrolyte solution used in electrodepositing the alloy coating. One such development is reported in the Bonn et al. U.S. Pat. No. 2,644,787. This patent, in general, describes a ferromagnetic coating which is produced by a combination of electrodeposition and chemical reduction from a electrolyte containing cobalt, nickel and hypophosphite ions. While many investigators have reported processes by which the coercivity of cobalt-nickel alloys may be increased, there have been few claims of an ability to produce predicted coercivities over a wide range of values. It is generally reported that remanence decreases with increasing coercivity and few, if any, investigators report remanence values in excess of 5,000 gausses with coercivities of 300 oersteds or greater.

Since coercivity is such an important property of a ferromagnetic coating for use in high density binary recording, a method of depositing a coating which provides for control of the coercivity of the resultant coating to predicted values over a wide range is highly desirable. Similarly, it is also greatly to be desired that the resultant coating exhibit relatively high values of squareness ratio and very high values of remanence.

SUMMARY OF THE INVENTION The processes for plating high-density magnetic recording films require critical concentrations and other operating conditions in the process. Yet there is not any organized body of knowledge from which processes for fabrication of high-densi ty recording media can be designed and the procedures in this area are largely empirical. It is quite clear that alloy films which are suitable for such applications are far more than simple electrodeposits of stated compositions. It has been found that alloys having very similar compositions and even very similar 60-cycle hysteresis characteristics as the present invention perform quite differently as high-density recording media. It is therefore suspected that the differences in the alloys obtained from the present invention which influence the performance at high recording densities are in the metallurgical and magnetic structures of the deposits.

The basic form of the present invention provides an improved method of depositing a ferromagnetic coating, having superior high-density recording qualities over those heretofore known. The improved method involves deposition solely through electrolytic action, by which the coercivity of the resultant coating can be predicted by controlling the composition of the electrolyte. The method of the present invention is inexpensive and very rapidly produces ferromagnetic coatings. A coating suitable for high-density binary recording applications is deposited in a period of time on the order of l minute. In particular, the method of the present invention allows the coercivity of a ferromagnetic carrier to be controlled and predicted through the control of the quantity of hypophosphite ions that is placed in the electrolyte to produce a coating which permits high recording densities, on the order of 2,000 binary bits per inch, that are readily reproducible. The pH of the plating bath is maintained in the range of 3.2 to 5.0 and the current density at the cathode is maintained in the range of l to 120 amperes per square foot.

The aforementioned basic form of the present invention is of considerable importance to high-density recording techniques and is a significant stride forward in the art of plating high-density magnetic recording films. However, it has become necessary to plate films capable of recording at even high densities in the order of 3,000 bits per inch and higher. This also can be achieved in accordance with the aforementioned basic form of the invention by increasing the concentration of hypophosphite ions in the bath.

However, a problem has arisen in commercial production facilities in making recording films. The problem arises due to the fact that the surfaces of the metallic anodes which are suitable for use in the electrodeposition of ferromagnetic recording films of cobalt-phosphorus and cobalt-nickelphosphorus alloys are catalytic to the oxidation of hypophosphite ion to phosphite ion in the Therefore, therefore, frequent analysis and adjustment of the hypophosphite ion concentration of the electrolyte is necessary to maintain the concentration of hypophosphite and phosphite ions at concentrations which will produce a constant coercivity of the recording films being deposited from one run to the next. Thus, it will be seen that an electrolyte prepared with hypophosphite ions along will soon have phosphite ions which have been oxidized from the hypophosphite ions. Hypophosphite ions are to 30 times as an effective source of phosphorus as phosphite ions therefore the phosphorus and hence the coercivity of the film will change markedly as the hypophosphite ions oxidize to phosphite ions.

It has now been determined that, at least in the presence of hypophosphite ion, phosphite ion may be employed as a partial source of phosphorus for electrodeposition of cobaltphosphorus and cobalt-nickel-phosphorus alloys from these baths. Therefore, high coercivity recording films may be electrodeposited from electrolyte containing a smaller concentration of hypophosphite ion that would be required if hypophosphite ion alone is employed as the source of phosphorus. It has further been determined that recording films deposited from baths which employ both hypophosphite and phosphite ions as sources of phosphorus are, in fact, as suitable for high-density magnetic recording media as are those deposited from baths which employ only hypophosphite ion as a source of phosphorus. Since the rate of oxidation of hypophosphite ion to phosphite ion at the catalytic surfaces is proportional to the concentration of hypophosphite ion in the bath and since phosphite ion is not oxidized at the catalytic surfaces, employment of both hypophosphite and phosphite ions as sources of phosphorus to reduce the concentration of hypophosphite ion required for a given coercivity provides a bath which demonstrates a greater chemical stability in the presence of the catalytic surfaces of the anodes.

The resulting chemical stability is important because the characteristics of the film being plated must be accurately matched to the characteristics of the magnetic recording heads used to record on the recording films. As a result, the coercivity must be accurately reproduced from one plating run to the next. Control has been achieved using the process in accordance with the basic form of the present invention by control over the concentration of hypophosphite ions in the electrolyte. However, the control of the hypophosphite ions alone becomes quite difi'lcult for higher density recording films in the order of 3,000 bits per inch and higher.

Thus, an improved method or process in accordance with the present invention utilizes phosphite ions in addition to hypophosphite ions in the plating bath and the concentration of the phosphite ions (as well as the concentration of the hypophosphite ions) are controlled. The hypophosphite ions are controlled within the range of 0 to 4 grams/liter for a cobalt-phosphorus film and within the range of O to 2.0 grams/liter for a cobalt-nickel-phosphorus film. The phosphite ions are controlled within the range of 0 to 12 grams/liter. Preferably the ratio of hypophosphite ions to phosphite ions in the bath is less than 1 to 7 for cobalt-nickel-phosphorus films and 2 to 7 for cobalt-phosphorus films.

In this manner a process is obtained which may be used to reproduce films having the same coercivity from one run to the next much more easily. Thus, a significant improvement is achieved even over the basic invention disclosed herein.

It should be noted that the recording densities in the order of 2,000 and 3,000 binary bits per inch have been achieved from processes in accordance with the present invention with the recording heads spaced up to 100 microinches from the recording film. This is important as it is much more difiicult to achieve higher recording densities when the recording head is spaced away from the recording film than when the recording head is in contact.

DESCRIPTION OF THE PREFERRED EMBODlMENT The ferromagnetic coating produced by the method of the present invention may consist of cobalt and small amounts of phosphorus when deposited from an electrolyte made up principally of cobalt, or of a cobalt-nickel alloy containing small amounts of phosphorus when deposited from an electrolyte having cobalt and nickel as the principal constituents. The cobalt-nickel alloys may contain up to 25 percent of nickel.

In carrying out the invention, the substrate or the carrier for the ferromagnetic coatings is utilized as the cathode in an electrolytic plating cell. The carrier may be composed of any of the well-known nonferromagnetic materials, such as the brasses bronzes, aluminum and aluminum alloys and magnesium and magnesium alloys; of ferromagnetic material over which is deposited or laminated a nonferromagnetic material or of a nonconductive material over which is deposited or laminated a conductive nonferromagnetic material. To this same end, the anode for the electrolytic cell is characterized as constructed of the principal elements of the bath and in a cobalt-nickel process may be constructed of an alloy of percent cobalt and 20 nickel. Alternatively, the anode material may be pure cobalt or pure nickel with the other element being added to the electrolyte proper as a salt of the metal. For example, if a pure cobalt anode is utilized, a nickel salt is added to the electrolyte and the electrolyte is diluted at intervals to maintain the proper composition of nickel and cobalt. Of course, the remaining constituents of the bath must also be added to the electrolyte when dilution is carried out to maintain the proper composition of the electrolyte. The electrodes are connected in a direct current circuit in the conventional fashion to cause the electrolytic action to produce the deposit at the cathode functioning as the magnetic coating. The composition of the electrolyte is as follows:

Cobalt-Nickel Alloy Deposition Ranges of Composition Cobaltous ions, Co as Cobaltous sulfate, C080, l040 g./l. Nickelous lons, Ni. as Nickelous sulfate, NiSO, [0-40 g./l. Additional Sulfate lons, S0." as the salt of Na, K, Ca or NH 0-25 g./l. Formate lons, CHOf', as the salt of Na, K, Ca or NH, or Ni 0-30 g./l. Boric Acid, H,BO= 0-60 gJl.

Hypophosphite lons, H,PO, as the While electrolytes having compositions within the ranges stated above provide satisfactory performance in the deposition of ferromagnetic coatings for use in binary recording applications, the preferred compositions of the electrolytes are as follows:

Cobalt-Nickel Alloy Deposition Ranges of Composition Cobaltous lons, Co, as Cobaltous Sulfate, C080 Nickelous Ions, Ni, as Nickelous Sulfate, NiSO, Additional Sulfate lons, S0,", as Na,SO, Formate lons, CHO{, as NaCHO, Boric Acid, H 80; Hypophosphite lons, H PO,a-, as NaH,FO,* 0-2.75 g./1.-0.0-0.04N

*From the standpoints of cost and availability, the sodium salt is preferred.

-20 g./l.0.333-0.444N 30-40 g./l.1.46-1.94N

Cobalt Deposition Ranges of Composition Cobaltous lons, Co, as cohaltous sulfate, CoSO, Additional Sulfate Ions, S0,, as Na,SO, Formate lons, CHO{, as NaCHO, Boric Acid, B0; Hypophosphite lons, H,PO,a-, as NaH,PO,* 0-6 g./1.-0.00.09N

From the standpoint ofcost and availability, the sodium salt is preferred.

The above electrolytes may have a pH within the range of 3,2 to 5.0 and, preferably have a pH of 3.8 which is maintained in a stable condition by the additon of sulfuric acid, H 80 The cathode current density applied through the electrodes may vary from 10 to 120 amperes per square foot. The temperature is maintained in the range of 90 to 140 F. and, preferably, should be maintained in the range of 100 to 110 F. The ferromagnetic coatings which are deposited on the cathodes may have thicknesses of 10 to 500 millionths of an inch. When the coatings are to be used for high-density binary recording, the preferred thickness is of the order of 50 millionths of an inch. Thicknesses of 5 millionths of an inch may be desirable as higher density recordings are achieved.

When the above defined aqueous electrolytes include sulfate, it is added to improve the electrical conductivity thereof while the boric acid is used in the conventional fashion as a buffer to stabilize the pH of the solution. When formate is included, it is added as a brightener. Although the electrolytes and the resulting deposits are improved through the use of these elements, it will be noted from the above charts that they may eliminated and satisfactory deposits obtained without them.

hypophosphite ions. At this minimum coercivity, the remanence is at a maximum.

An important feature of the invention is that it has been found that the coercivity of the deposited ferromagnetic coat ing may not only be controlled but predicted by controlling the amount of phosphorus that is added to the electrolyte and particularly phosphorus in the form of a hypophosphite ion. To this end, it has been found that the coercivity of the deposited ferromagnetic coating increases as the amount of hypophosphite ion in the electrolyte is increased. In coatings having the minimum coercivities, the remanence is 13,000 to 15,000 gausses. With the addition of hypophosphite ions to the electrolyte, it has been found that with an increase in the coercivity to 300 oersteds the remanence decreases to 8,500 to 10,000 gausses and then stays approximately constant as the coercivity is further increased.

When utilizing the above defined electrolytes at a temperature of l0O-l 10 F. and using a cathodic current density of 60 amperes per square foot, the coercivity of the deposited coating can be controlled to achieve preselected values in the range of to 800 oersteds for cobalt nickel alloy deposits and in the range of 60 to 700 oersteds for cobalt coatings.

In accordance with the present invention the deposited ferromagnetic coating assumes the composition of the essential elements in the electrolyte but, in the case of cobalt-nickel alloys, not in the same proportions as these elements are present in the electrolyte. Accordingly, the ferromagnetic coatings produced by the present invention may comprise essentially cobalt or cobalt-nickel alloys as these elements are present in the electrolyte and small amounts of phosphorus.

improved results are derived through the use of the hypophosphite ion in the electrolyte of the present invention to thereby cause the coating to exhibit an increased coercivity. The amount of hypophosphite ion and thereby the coercivity may be increased. 1

Although it would appear that other elements having similar characteristics to phosphorus may be added to the bath, it has been found that elements such as sulfur, selenium and tellurium do not produce these advantageous results.

It will be obvious to those skilled in the art that a pure electrolytic plate will occur in accordance with the present invention only when the stability constant of the metal ions is sufficiently high to prevent chemical deposition. Therefore, if any complexing agent is introduced into the bath, such as ammonium, care must be exercised to prevent a sufficiently low stability constant as will cause chemical deposition and which will prevent deposition solely by electrolysis.

Hypophosphite ions, as the source of phosphorus in the process of the present invention, are felt to be important in producing the high density magnetic recording films.

The composition of an electrolyte utilizing a combination of hypophosphite ions and phosphite ions in accordance with the improved form of the present invention is as follows:

Cobalt-Nickel-Phosphorus Alloy Deposition Ranges of Composition Cobaltous Ions, CO", as Cobaltous sulfate, CoSO 10-50 g./l. Nickelous ions, Ni, as Nickelous sulfate, NiSO, 10-50 g.l|. Ratio of Nickel Cobalt ions in the bath 0.95-1.15 gJl. Additional Sulfate lens, 50., as the salt of Na, K, Ca or NH, 0-12 gJl. Formate Ions, COOH', as HCOOH or as the salt of Na, K, Ca, NH or Ni 0-20 g./lv Boric Acid, H 80, 0-40 g.ll. Phosphite Ions, H,PO=', as the salt of Na, K, Ca, NH. or as H PO, 0-12 g./l. Hypophosphite lons, H,P0,', as the salt of Na, K, Ca, NH, or as H ,PO, 0-2.0 g./1.

Cobalt-Phosphorus Alloy Deposition Ranges of Composition Cohaltous Ions, CO", as Cobaltous sulfate, CnSO, 20-80 g./l. Additional Sulfate Ions, 80,, as the salt of Na, K, Ca, or NH, -12 g./l. Formate Ions, COOH, as HCOOH or as the salt of Na, K, Ca, NH, or Ni 0-20 gJl. Boric Acid, H ,BO, 0-40 g./l. Phosphitc Ions, H,PO,, as the salt ofNa, K, Ca. NH, or as H,PO, 0-12 g./l, Hypophosphite Ions, H,PO{ or as the salt of Na, K. Ca, NH, or as H PO, 0-4.0 g./l.

While electrolytes having compositions within the ranges stated above provide satisfactory performance in the deposition of magnetic recording films, the preferred ranges providing markedly superior results are as follows:

Cobalt-Nickel Phosphorus Alloy Deposition Ranges of Composition Cobaltous Ions, Co", as Cobaltous sulfate CoSO, 20-50 gJl. Nickelous Ions, Ni, as Nickelous sulfate, M80, 20-50 g./l. Ratio of Nickel to Cobalt Ions in the bath 0.95-1.15 Additional Sulfate Ions, SO, as the salt of Na, K, Ca or NH, 0-12 g./l. Formatc Ions, COOH as HCOOH or as the salt of Na, K, Ca, NH or Ni 0-20 3.. Boric Acid, H 80, 0-40 g./l. Phosphitc Ions, H,PO{, as the salt of Na, K, Ca, NH, or as H,PO 7.5-12 g./l. Hypophosphite Ions, H,PO{, as the salt ofNa, K, Ca, NH or as H PO, 0-l.10 g./l. 5

Cobalt-Phosphorus Alloy Deposition The aforementioned electrolytes must have a pH in the range of 3.2 to 5.0 or preferably a pH of 3.8 maintained by addition of nickel, potassium, or sodium carbonate or sulfuric acid, as required to maintain the chosen value. The cathode current density should be maintained in the range of 10-120 amperes per square foot with a temperature in the range of 90-140bL F. Preferably the temperature is maintained in the range of 100 to 110 F.

The bath is preferably agitated adjacent to the surface being plated for high density recording films.

With reference to the foregoing tables it will be seen that the preferred ratio of hypophosphite ions to phosphite ions is less than 1 to 7 for cobalt-nickel-phosphorus films and less than 2 to 7 for cobalt-phosphorus films. With these preferred ranges, the change in hypophosphite ions due to oxidation does not appreciably change the phosphorus and hence the coercivity in the resulting film. This is due to the much greater contribution to phosphorus by the phosphite ions.

Recording media matched to the characteristics of recording equipment of a given design for use in a high-density digital recording application were deposited in the equipment employed by the inventor from electrolyte solutions of the following compositions:

Cobalt-Nickel-Phosphorus Alloy Deposition Ranges of Composition Cobaltous Ions, Co", as cobultous sulfate, C050 25 g./l. Nickelous Ions, Ni", as nickelous sulfate, NiSO, 28 gJI. Ratio of Nickel to Cobalt Ions in the bath 1 to 2 Additional Sulfate Ions, S0,", as Nu,SO. 8.0 g./|. Formate Ions, COOH', as NaCOOH 20.0 g./l. Boric Acid, H,BO 30.0 3.11. Phosphite Ions, H,PO,, as NaHJO, 12.0 g./l. Hypophosphite Ions, H,PO,' as NaH,PO 1.05 g./I.

Cobalt-Phosphorus Alloy Deposition Ranges of Composition Cobaltous Ions, Co, as Cobaltous sulfate, C050. 50 g./l. Additional Sulfate Ions, S0,", as Na,S0, 8.0 g./l. Formate Ions, COOH', as NaCOOH 20 g./l. Boric Acid, H ,B0, 30 g./l. Phosphite Ions, H,PO,, as NaH P0, 12 71. Hypophosphitt: Ions, H,PO, as NaH,PO, 1.7 g./l.

Recording films were deposited from the aforementioned two electrolytes at a pH of 3.8, a temperature of F. and a current density of 45 amperes per square foot.

The control described herein is achieved by analysis of the electrolyte using conventional techniques to determine the concentrations of hypophosphite ions and phosphite ions. The control also involves adjusting the concentrations of hypophosphite ions and phosphite ions so that a predetermined desired coercivity is achieved. When adjusting the phosphite ion concentration by addition of phosphorous acid, it is preferred to neutralize the phosphorus acid to the pH of the rest of the electrolyte before addition to the bath. It should be noted that the predetermined coercivity is preferably a single value but may be a relatively small range of coercivities within the tolerances of the magnetic recording and reading heads and the associated electronic circuitry to be used therewith. This range of permissible coercivities is smaller at higher recording densities than at lower recording densities.

The adjustment of the hypophosphite ions may be accomplished by adding hypophosphite ions to the electrolyte from time to time as needed, as the hypophosphite ions oxidize. The adjustment of the phosphite ions may be accomplished by diluting the electrolyte from time to time as needed to maintain the concentration of phosphite ions, in proportion to the hypophosphite ions, at a level where the predetermined coercivity is obtained. Alternatively the phosphite ions may be removed to reduce the concentration.

Since the effect of phosphite ions on phosphorus or coercivity in the film is much less than hypophosphite ions, adjustment may also include addition of hypophosphite ions to the electrolyte from time to time as required to maintain a prefixed concentration thereof and allowing the phosphite ions to build up from an initial value to a maximum value at which time the electrolyte is replaced.

Although the ranges of hypophosphite ions and phosphite ions given in some of the examples start with 0, it will be understood that this value is given as a limit and that there must be some phosphite ions or hypophosphite ions present as the case may be.

Although one example of the present invention has been shown by way of illustration, it should be understood that there are many other rearrangements and embodiments of the present invention within the scope of the following claims.

What is claimed is:

1. The method for the deposition of a ferromagnetic recording film on an electrically conductive carrier comprising subjecting the carrier as cathode to a current density of between l and 120 amperes per square foot in an aqueous electrolyte having a pH of 3.2 to 5.0 wherein the aqueous electrolyte consists essentially of:

Cobaltous ions derived from cobaltous sulfate Nickelous ions derived from nickelous sulfate Additional sulfate ions derived from sodium sulfate Formate ions derived from sodium formate to g.ll. (0.3330.444N) Boric Acid to g./l,(l.46-l .94N)

and a source of phosphorus, the source of phosphorus comprising at least some hypophosphite ions up to 2.75 grams per liter, derived from sodium hypophosphite; the bath being maintained at a temperature in the range of 100 F.

2. The method for deposition of a ferromagnetic recording film on an electrically conductive carrier comprising:

a. immersing the carrier as cathode in an aqueous electrolyte comprising cobaltous ions in the range of 20 to 80 grams per liter and a source of phosphorus, the source of phosphorus comprising at least some hypophosphite ions up to 4 grams per liter and phosphite ions in the range of from 7.5 to 12 grams per liter 7 b. maintaining the pH of the electrolyte at a value of from c. maintaining the temperature of the electrolyte in the range of from 90 to 140 F.; and

d. applying to the cathode a current density of from about 10 to l20 amperes per square foot and thereby codeposit phosphorus and cobalt on the conductive carrier.

3. The method of claim 2 wherein the cobaltous ions are derived from cobaltous sulfate and wherein the hypophosphite ions are derived from hypophosphorus acid or the sodium, potassium, calcium, or ammonium salt thereof.

4. The method of claim 2 wherein the electrolyte is maintained within a temperature range of from l00 to 1 10 F.

5. The method of claim 2 wherein the cobaltous ions are derived from cobaltous sulfate and wherein the hypophosphite ions are derived from hypophosphorous acid or the sodium, potassium, or calcium salt thereof and the phosphite ions are derived from phosphorous acid or the sodium, potassium, or calcium salt thereof.

6. The method for the deposition of a ferromagnetic recording film on an electrically conductive carrier comprising subjecting the carrier as cathode to a current density of between 10 and 120 amperes per square foot in an aqueous electrolyte having a pH of from 3.2 to 5.0 and consisting essentially of: cobaltous ions in the range of 20 to 80 grams per liter, at least some hypophosphite ions and phosphite ions; and controlling the hypophosphite ions in the range up to 4 grams per liter and the phosphite ions in the range of 7.5 to 12 grams per liter to obtain a recording film having a predetermined coercivity, the phosphite ions reducing the concentration of hypophosphite ions required for the predetermined coercivity.

7. The method defined in claim 6 wherein the phosphite ions are derived from phosphorus acid or the sodium, potassium, calcium or ammonium salt thereof.

8. The method defined in claim 7 wherein the phosphorus acid is neutralized to the pH of the rest of the electrolyte before addition thereto.

9. The method defined in claim 6 wherein the ratio of hypophosphite ions to phosphite ions is less than 2 to 7.

10. The method defined in claim 6 wherein the hypophosphite ions are derived from hypophosphorus acid or the sodium, potassiumcalcium or ammonium salt thereof.

11. The method defined in claim 6 wherein the cobalt ions are derived from cobaltous sulfate.

12. The method for deposition of a ferromagnetic recording film on an electrically conductive carrier, comprising subjecting the carrier as cathode to a current density of between 10 and l20 amperes per square foot in an aqueous electrolyte having a pH of from 3.2 to 5.0, a temperature in the range of 20 to 25 g./l. (0.6790.848N) 20 to 25 gJl. (0.68l0.852N) from about to l40 F., and consisting essentially of: cobaltous ions in the range of l0 to 50 grams per liter, nickelous ions in the range of 10 to 50 grams per liter, and at least some hypophosphite ions and phosphite ions; and controlling the hypophosphite ions in the range up to 2 grams per liter and the phosphite ions in the range of 7.5 to 12 grams per liter to obtain a recording film having a predetermined coercivity, the phosphite ions reducing the concentration of hypophosphite ions required for the predetermined coercivity.

13. The method defined in claim 12 wherein the phosphite ions are derived from phosphorus acid or the sodium, potassium calcium or ammonium salt thereof.

14. The method defined in claim 13 wherein the phosphorus acid is neutralized to the pH of the rest of the electrolyte before addition thereto.

15. The method defined in claim 12 wherein the ratio of hypophosphite ions to phosphite ions is less than 1 to 7.

16. The method defined in claim 12 wherein the hypophosphite ions are derived from hypophosphorus acid or the sodium, potassium, calcium, or ammonium salt thereof.

17. The method defined in claim 12 wherein the cobaltous ions are derived from cobaltous sulfate and the nickelous ions are derived from nickelous sulfate.

18. The method defined in claim 12 wherein the hypophosphite ions are derived from hypophosphorous acid or the sodium, potassium, or calcium salt thereof.

19. The method defined in claim 12 wherein the phosphite ions are derived from phosphorous acid or the sodium, potassium, or calcium salt thereof.

20. The method for the deposition of a magnetic recording film on an electrically conductive carrier comprising subjecting the carrier as cathode to a current density of between 10 and amperes per square foot in an aqueous electrolyte having a pH of from 3.2 to 5.0 and consisting essentially of: cobaltous ions in the range of 20 to 80 grams per liter, at least some hypophosphite ions and phosphite ions; and controlling the hypophosphite ions in the range up to 2 grams per liter and the phosphite ions in the range of 7.5 to 12 grams per liter to obtain a recording film having a predetermined coercivity, the phosphite ions reducing the concentration of hypophosphite ions required for the predetermined coercivity.

21. The method defined in claim 20 wherein the hypophosphite ions are derived from hypophosphorus acid or the sodium, potassium, calcium, or ammonium salt thereof.

22. The method defined in claim 21 wherein the phosphite ions are derived from phosphorous acid or the sodium, potassium, calcium or ammonium salt thereof.

23. The method defined in claim 22 wherein the phosphorus acid is neutralized to the pH of the rest of the electrolyte before addition to the bath.

24. A method as defined in claim 20 wherein the cobalt ions are in the range of 40 to 80 grams per liter.

25. The method for the electrolytic deposition of a ferromagnetic recording film on an electrically conductive carrier, comprising subjecting the carrier as cathode to a current density of between 10 and 120 amperes per square foot in an aqueous sulfate electrolyte having a pH of from 3.2 to 5.0, a temperature in the range of from about 90 to F., and consisting essentially of: cobaltous ions in the range of 10 to 50 grams per liter, nickelous ions in the range of l0 to 50 grams per liter, and at least some hypophosphite ions and phosphite ions; and controlling the hypophosphite ions in the range up to 1.10 grams per liter and the phosphite ions in the range of 7.5 to 12 grams per liter to obtain a recording film having a predetermined coercivity, the phosphite ions reducing the concentration of hypophosphite ions required for the predetermined coercivity.

26. The method defined in claim 25 wherein the hypophosphite ions are derived from hypophosphorus acid or the sodium, potassium, calcium, or ammonium salt thereof.

27. The method defined in claim 26 wherein the phosphite ions are derived from phosphorus acid or the sodium, potassium, calcium, or ammonium salt thereof.

28. The method defined in claim 26 wherein the phosphite ions are derived from phosphorous acid or the sodium, potassium, or calcium salt thereof.

29. A method as defined in claim 25 wherein the cobaltous ions are present in a range of 20 to 50 grams per liter and the nickelous ions are present in a range of 20 to 50 grams per liter.

30. The method defined in claim 25 wherein the electrolyte includes at least some formate ions derived from the sodium, potassium, or calcium salt of formic acid in the range up to 20 grams/liter.

31. The method defined in claim 25 wherein the hypophosphite ions are derived from hypophosphorous acid or the sodium, potassium, or calcium salt thereof.

32. The method for the deposition of a ferromagnetic recording film on an electrically conductive carrier comprising subjecting the carrier as cathode to a current density of between 10 and 120 amperes per square foot in an aqueous electrolyte having a pH in the range of 3.2 to 5.0 and consisting essentially of:

Cobaltous ions, derived from cobaltous sulfate 20 to 80 g./l. Additional sulfate ions as the sodium, potassium,

calcium, or ammonium salt of sulfuric acid to [2 gJl. Formate ions derived from the sodium, potassium,

calcium, or ammonium salt of the formic acid 0 to 20 g./l. Boric acid 0 to 40 g./l.

at least some hypophosphite ions derived from hypophosphorous acid or the sodium, potassium, calcium or ammonium salt thereof and phosphite ions derived from phosphorous acid or the sodium, potassium, calcium, or ammonium salt thereof and absent sufficient ammonium ions to cause chemical deposition and controlling the hypophosphite ions within the range up to 4.0 grams per liter and the phosphite ions within the range of 7.5 to 12 grams per liter to obtain a recording film having a predetermined coercivity, the phosphite ions reducing the concentration of hypophosphite ions required for the predetermined coercivity.

33. The method defined in claim 1 wherein the temperature is maintained in the range of 90 to 140 F.

34. The method for the deposition of a ferromagnetic recording film on an electrically conductive carrier comprising subjecting the carrier as cathode to a current density of between and 120 amperes per square foot in an aqueous electrolyte having a pH in the range of 3.2 to 5.0 and consisting essentially of:

Cohaltous ions as cobaltous sulfate 40 to 80 g./l.

Additional sulfate ions as sodium sulfate 0 to l2 gJl.

Formatc ions as sodium formate 0 to 20 g.ll.

Boric acid 0 to 40 g./l.

at least some hypophosphite ions derived from hypophosphorous acid or the sodium, potassium, calcium or ammonium salt thereof, and phosphite ions derived from phosphorus acid or the sodium, potassium, calcium or ammonium salt thereof and absent sufficient ammonium ions to cause chemical deposition; and controlling the hypophosphite ions within the range up to 2.0 grams per liter and the phosphite ions within the range of 7.5 to 12 grams per liter to obtain a recording film having a predetermined coercivity, the phosphite ions reducing the concentration of hypophosphite ions required for the predetermined coercivity.

35. The method defined in claim 34 wherein the concentrations are as follows:

Cobaltous ions 50 3.1L Hypophosphite ions l.7 g./l. Phosphite ions l2 gJl.

36. The method defined in claim 35 wherein the pH of the electrolyte is 3.8.

37. The method defined in claim 34 wherein the bath is maintained at a temperature in the range of to l 10 F.

38. The method for the electrolytic deposition of a ferromagnetic recording film on an electrically conductive carrier comprising subjecting the carrier as cathode to a current density of between 10 and amperes per square foot in an aqueous electrolyte having a pH of 3.2 to 5.0, a temperature in the range of from 90 to F., and consisting essentially of:

Cobaltous ions derived from cobaltous sulfate 10 to 50 g./l. Nickclous ions derived from nickelous sulfate ID to 50 g./l. Additional sulfate ions derived from the sodium,

potassium, or calcium, salt of sulfuric acid 0 to l2 gJl. Formate ions as the sodium, potassium, or

calcium, nickel salt of formic acid 0 to 20 g./l. Boric acid 0 to 40 g/l.

at least some hypophosphite ions, derived from hypophosphorous acid, or the sodium, potassium, or calcium salt thereof and phosphite ions derived from phosphorous acid or the sodium potassium, or calcium salt thereof, and absent sufficient ammonium ions to cause chemical deposition and controlling the hypophosphite ions within the range up to 2.0 grams/liter and the phosphite ions within the range of from 7.5 to 12 grams/liter to obtain a recording film having a predetermined coercivity, the phosphite ions reducing the concentration of hypophosphite ions required for the predetennined coercivity.

39. The method for the deposition of a ferromagnetic recording film defined in claim 38 wherein the aqueous electrolyte consists essentially of:

Cubaltous ions derived from cobaltous sulfate 2010 50 g./l. Nickelous ions derived from nickelous sulfate 20 to S0 g./l.

and the hypophosphite ions are maintained in the range up to 1.10 grams/liter.

40. The method defined in claim 39 wherein temperature of the bath is maintained in the range of 100 to 1 10 F.

41. The method defined in claim 39 wherein the concentrations are as follows:

Cobaltous ions 25 g./l. Nickelous ions 28 g./l. Hypophosphite ions 1.05 g./l. Phosphite ions 12 g./l.

22 3 UNITED STATES PATENT GFFICE D 4 CERTIFICATE OF CORREC'HON patent 3,637,471 b ted January .25, 1972 Ifiventofls) lohn P. Faulgnei: I v

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

2 delete and insert as before "H 1 0 line a 2 line 132-, delete ".a' 'aa'iferl'fHgPOQfr'. line 33; 'df1e. ",.13". we 21, "100" should be --110-;-

line 44, "'coonff'" should be "0 011 line 59, delete "DL" after 14 0" efid insert line 29', "100" should be -1 1o. 1

(:51, linelf, add, to 1 0w 001'. 1'1, 1i e 33, "claim 1" should BB -Dam 32-;

Signed and sealed t is 22nd day of August 1972.

- (SEAL) Attes'tz- EDWARD ME-LDTCHDR R; ROBERT GOTTSCHALK Attesting Officer 7 Commissioner of Patents 

2. The method for deposition of a ferromagnetic recording film on an electrically conductive carrier comprising: a. immersing the carrier as cathode in an aqueous electrolyte comprising cobaltous ions in the range of 20 to 80 grams per liter and a source of phosphorus, the source of phosphorus comprising at least some hypophosphite ions up to 4 grams per liter and phosphite ions in the range of from 7.5 to 12 grams per liter b. maintaining the pH of the electrolyte at a value of from 3.2 to 5.0; c. maintaining the temperature of the electrolyte in the range of from 90* to 140* F.; and d. applying to the cathode a current density of from about 10 to 120 amperes per square foot and thereby codeposit phosphorus and cobalt on the conductive carrier.
 3. The method of claim 2 wherein the cobaltous ions are derived from cobaltous sulfate and wherein the hypophosphite ions are derived from hypophosphorus acid or the sodium, potassium, calcium, or ammonium salt thereof.
 4. The method of claim 2 wherein the electrolyte is maintained within a temperature range of from 100* to 110* F.
 5. The method of claim 2 wherein the cobaltous ions are derived from cobaltous sulfate and wherein the hypophosphite ions are derived from hypophosphorous acid or the sodium, potassium, or calcium salt thereof and the phosphite ions are derived from phosphorous acid or the sodium, potassium, or calcium salt thereof.
 6. The method for the deposition of a ferromagnetic recording film on an electrically conductive carrier comprising subjecting the carrier as cathode to a current density of between 10 and 120 amperes per square foot in an aqueous electrolyte having a pH of from 3.2 to 5.0 and consisting essentially of: cobaltous ions in the range of 20 to 80 grams per liter, at least some hypophosphite ions and phosphite ions; and controlling the hypophosphite ions in the range up to 4 grams per liter and the phosphite ions in the range of 7.5 to 12 grams per liter to obtain a recording film having a predetermined coercivity, the phosphite ions reducing the concentration of hypophosphite ions required for the predetermined coercivity.
 7. The method defined in claim 6 wherein the phosphite ions are derived from phosphorus acid or the sodium, potassium, calcium or ammonium salt thereof.
 8. The method defined in claim 7 wherein the phosphorus acid is neutralized to the pH of the rest of the electrolyte before addition thereto.
 9. The method defined in claim 6 wherein the ratio of hypophosphite ions to phosphite ions is less than 2 to
 7. 10. The method defined in claim 6 wherein the hypophosphite ions are derived from hypophosphorus acid or the sodium, potassium, calcium or ammonium salt thereof.
 11. The method defined in claim 6 wherein the cobalt ions are derived from cobaltous sulfate.
 12. The method for deposition of a ferromagnetic recording film on an electrically conductive carrier, comprising subjecting the carrier as cathode to a current density of between 10 and 120 amperes per square foot in an aqueous electrolyte having a pH of from 3.2 to 5.0, a temperature in the range of from about 90* to 140* F., and consisting essentially of: cobaltous ions in the range of 10 to 50 grams per liter, nickelous ions in the range of 10 to 50 grams per liter, and at least some hypophosphite ions and phosphite ions; and controlling the hypophosphite ions in the range up to 2 grams per liter and the phosphite ions in the range of 7.5 to 12 grams per liter to obtain a recording film having a predetermined coercivity, the phosphite ions reducing the concentration of hypophosphite ions required for the predetermined coercivity.
 13. The method defined in claim 12 wherein the phosphite ions are derived from phosphorus acid or the sodium, potassium calcium or ammonium salt thereof.
 14. The method defined in claim 13 wherein the phosphorus acid is neutralized to the pH of the rest of the electrolyte before addition thereto.
 15. The method defined in claim 12 wherein the ratio of hypophosphite ions to phosphite ions is less than 1 to
 7. 16. The method defined in claim 12 wherein the hypophosphite ions are derived from hypophosphorus acid or the sodium, potassium, calcium, or ammonium salt thereof.
 17. The method defined in claim 12 wherein the cobaltous ions are derived from cobaltous sulfate and the nickelous ions are derived from nickelous sulfate.
 18. The method defined in claim 12 wherein the hypophosphite ions are derived from hypophosphorous acid or the sodium, potassium, or calcium salt thereof.
 19. The method defined in claim 12 wherein the phosphite ions are derived from phosphorous acid or the sodium, potassium, or calcium salt thereof.
 20. The method for the deposition of a magnetic recording film on an electrically conductive carrier comprising subjecting the carrier as cathode to a current density of between 10 and 120 amperes per square foot in an aqueous electrolyte having a pH of from 3.2 to 5.0 and consisting essentially of: cobaltous ions in the range of 20 to 80 grams per liter, at least some hypophosphite ions and phosphite ions; and controlling the hypophosphite ions in the range up to 2 grams per liter and the phosphite ions in the range of 7.5 to 12 grams per liter to obtain a recording film having a predetermined coercivity, the phosphite ions reducing the concentration of hypophosphite ions required for the predetermined coercivity.
 21. The method defined in claim 20 wherein the hypophosphite ions are derived from hypophosphorus acid or the sodium, potassium, calcium, or ammonium salt thereof.
 22. The method defined in claim 21 wherein the phoSphite ions are derived from phosphorous acid or the sodium, potassium, calcium or ammonium salt thereof.
 23. The method defined in claim 22 wherein the phosphorus acid is neutralized to the pH of the rest of the electrolyte before addition to the bath.
 24. A method as defined in claim 20 wherein the cobalt ions are in the range of 40 to 80 grams per liter.
 25. The method for the electrolytic deposition of a ferromagnetic recording film on an electrically conductive carrier, comprising subjecting the carrier as cathode to a current density of between 10 and 120 amperes per square foot in an aqueous sulfate electrolyte having a pH of from 3.2 to 5.0, a temperature in the range of from about 90* to 140* F., and consisting essentially of: cobaltous ions in the range of 10 to 50 grams per liter, nickelous ions in the range of 10 to 50 grams per liter, and at least some hypophosphite ions and phosphite ions; and controlling the hypophosphite ions in the range up to 1.10 grams per liter and the phosphite ions in the range of 7.5 to 12 grams per liter to obtain a recording film having a predetermined coercivity, the phosphite ions reducing the concentration of hypophosphite ions required for the predetermined coercivity.
 26. The method defined in claim 25 wherein the hypophosphite ions are derived from hypophosphorus acid or the sodium, potassium, calcium, or ammonium salt thereof.
 27. The method defined in claim 26 wherein the phosphite ions are derived from phosphorus acid or the sodium, potassium, calcium, or ammonium salt thereof.
 28. The method defined in claim 26 wherein the phosphite ions are derived from phosphorous acid or the sodium, potassium, or calcium salt thereof.
 29. A method as defined in claim 25 wherein the cobaltous ions are present in a range of 20 to 50 grams per liter and the nickelous ions are present in a range of 20 to 50 grams per liter.
 30. The method defined in claim 25 wherein the electrolyte includes at least some formate ions derived from the sodium, potassium, or calcium salt of formic acid in the range up to 20 grams/liter.
 31. The method defined in claim 25 wherein the hypophosphite ions are derived from hypophosphorous acid or the sodium, potassium, or calcium salt thereof.
 32. The method for the deposition of a ferromagnetic recording film on an electrically conductive carrier comprising subjecting the carrier as cathode to a current density of between 10 and 120 amperes per square foot in an aqueous electrolyte having a pH in the range of 3.2 to 5.0 and consisting essentially of: Cobaltous ions, derived from cobaltous sulfate 20 to 80 g./l. Additional sulfate ions as the sodium, potassium, calcium, or ammonium salt of sulfuric acid 0 to 12 g./l. Formate ions derived from the sodium, potassium, calcium, or ammonium salt of the formic acid 0 to 20 g./l. Boric acid 0 to 40 g./l. at least some hypophosphite ions derived from hypophosphorous acid or the sodium, potassium, calcium or ammonium salt thereof and phosphite ions derived from phosphorous acid or the sodium, potassium, calcium, or ammonium salt thereof and absent sufficient ammonium ions to cause chemical deposition and controlling the hypophosphite ions within the range up to 4.0 grams per liter and the phosphite ions within the range of 7.5 to 12 grams per liter to obtain a recording film having a predetermined coercivity, the phosphite ions reducing the concentration of hypophosphite ions required for the predetermined coercivity.
 33. The method defined in claim 32 wherein the temperature is maintained in the range of 90* to 140* F.
 34. The method for the deposition of a ferromagnetic recording film on an electricallY conductive carrier comprising subjecting the carrier as cathode to a current density of between 10 and 120 amperes per square foot in an aqueous electrolyte having a pH in the range of 3.2 to 5.0 and consisting essentially of: Cobaltous ions as cobaltous sulfate 40 to 80 g./l. Additional sulfate ions as sodium sulfate 0 to 12 g./l. Formate ions as sodium formate 0 to 20 g./l. Boric acid 0 to 40 g./l. at least some hypophosphite ions derived from hypophosphorous acid, or the sodium, potassium, calcium or ammonium salt thereof, and phosphite ions derived from phosphorus acid or the sodium, potassium, calcium or ammonium salt thereof and absent sufficient ammonium ions to cause chemical deposition; and controlling the hypophosphite ions within the range up to 2.0 grams per liter and the phosphite ions within the range of 7.5 to 12 grams per liter to obtain a recording film having a predetermined coercivity, the phosphite ions reducing the concentration of hypophosphite ions required for the predetermined coercivity.
 35. The method defined in claim 34 wherein the concentrations are as follows: Cobaltous ions 50 g./l. Hypophosphite ions 1.7 g./l. Phosphite ions 12 g./l.
 36. The method defined in claim 35 wherein the pH of the electrolyte is 3.8.
 37. The method defined in claim 34 wherein the bath is maintained at a temperature in the range of 100* to 110* F.
 38. The method for the electrolytic deposition of a ferromagnetic recording film on an electrically conductive carrier comprising subjecting the carrier as cathode to a current density of between 10 and 120 amperes per square foot in an aqueous electrolyte having a pH of 3.2 to 5.0, a temperature in the range of from 90* to 140* F., and consisting essentially of: Cobaltous ions derived from cobaltous sulfate 10 to 50 g./l. Nickelous ions derived from nickelous sulfate 10 to 50 g./l. Additional sulfate ions derived from the sodium, potassium, or calcium, salt of sulfuric acid 0 to 12 g./l. Formate ions as the sodium, potassium, or calcium, nickel salt of formic acid 0 to 20 g./l. Boric acid 0 to 40 g./l. at least some hypophosphite ions, derived from hypophosphorous acid, or the sodium, potassium, or calcium salt thereof and phosphite ions derived from phosphorous acid or the sodium potassium, or calcium salt thereof, and absent sufficient ammonium ions to cause chemical deposition and controlling the hypophosphite ions within the range up to 2.0 grams/liter and the phosphite ions within the range of from 7.5 to 12 grams/liter to obtain a recording film having a predetermined coercivity, the phosphite ions reducing the concentration of hypophosphite ions required for the predetermined coercivity.
 39. The method for the deposition of a ferromagnetic recording film defined in claim 38 wherein the aqueous electrolyte consists essentially of: Cobaltous ions derived from cobaltous sulfate 20 to 50 g./l. Nickelous ions derived from nickelous sulfate 20 to 50 g./l. and the hypophosphite ions are maintained in the range up to 1.10 grams/liter.
 40. The method defined in claim 39 wherein temperature of the bath is maintained in the range of 100* to 110* F.
 41. The method defined in claim 39 wherein the concentrations are as follows: Cobaltous ions 25 g./l. Nickelous ions 28 g./l. Hypophosphite ions 1.05 g./l. Phosphite ions 12 g./l. 